This invention relates to devices for conveying bodily fluids, and more particularly to body implantable left ventricle or whole heart assist pumps for bypassing the heart during open heart surgery, or to assist a disfunctional heart or left ventricle.
Centrifugal blood pumps have long been recognized for their utility as a supplement to or replacement for the human heart, for example in assisting a damaged left ventricle, for temporary heart bypass in the event that such is required in open heart surgery, and for total heart bypass when two such pumps are implanted. Such pumps operate continuously and at high speeds, for example in the range of 4,000 to 7,000 rpm, and are relatively small, which facilitates implantation.
A major problem with centrifugal blood pumps, however, is the need for a positive seal between the pump housing and the internal rotating means for pumping, e.g. the impeller and rotor. Conventional shaft seals are not effective when the involved fluid is blood, since blood is not suitable, either as a lubricant or as a cooling medium.
In recognition of these difficulties, centrifugal pumps have been designed to utilize a lubricant other than blood, for example a saline solution, along with a sealing means to prevent the passage of blood into lubricated areas. U.S. Pat. No. 4,135,253 (Reich et al) discloses an impeller pump in which a saline solution in a rotor housing floats the rotor. An elastomeric lip seal surrounds a shaft which couples the rotor and impeller. The saline solution is maintained at a positive pressure greater than the blood pressure on the opposite side of the seal, thus to prevent flow of blood into the rotor housing. However, the breaking pressure to establish a small flow across the seal is sufficiently high in some cases that the pump can start with little or no flow through the seal area. The dry seal heats and wears rapidly. Following such rapid wear, a flow of saline lubricates and cools the seal, substantially preventing further rapid wear, to initiate a slow wear phase tending to smooth the seal. The results of this wear process are unpredictable; at times satisfactory, at other times permitting excessive saline leakage into the blood stream, diluting the blood to an undesirable degree.
In U.S. Pat. No. 4,704,121 (Moise), an anti-thrombogenic blood pump features an impeller blood pump with seals lubricated by a saline solution, with saline perfusing from about a rotary impeller shaft into the blood conveying impeller chamber at a rate of about one cubic centimeter every twenty-four hours. The seal in the perfusion area can be a face seal, a cylindrical (journal) seal or a hybrid face/cylindrical seal. In each case, the seal is a restricted fluid passage between two rigid members, namely the rotating shaft and the impeller chamber wall, requiring strict tolerances for a clearance said to be typically in the order of 2.5 micrometers. Aside from high manufacturing cost, this arrangement provides no resistance to blood entry into the chamber containing the shaft in the event of any disruption in saline flow.
Therefore, it is an object of the present invention to provide a relatively low cost means for achieving an effective seal between an impeller chamber and a rotor chamber in a centrifugal blood pump.
Another object of the invention is to provide a pump for bodily fluids in which a flexible seal, deformable to permit a steady perfusion of a fluid lubricant from a rotor chamber into an impeller chamber, prevents passage of blood from the impeller chamber into the rotor chamber.
Another object is to provide a perfusion seal also effective to resist passage of blood, from an impeller chamber past the seal into a rotor chamber, in the event of a temporary interruption in the perfusion of the lubricant.
Yet another object of the invention is to provide a single source for a lubricant and fluid for a perfusion seal between the rotor and impeller chambers of a centrifugal pump, with lubricant supplied to the rotor chamber at a constant flow rate, independent of the rotational speed of the impeller.